A Westerbork 1415 MHz survey of radio sources. V. Spectrophotometric observations of a sample of the stellar identifications.
Abstract
Summary. Twenty-nine of the' optical identifications reported in Papers II and III have been observed with the multichannel spectrometer and/or the silicon image tube spectrograph on the 5 m telescope at Palomar. They were selected from the brighter optical identifications which appeared stellar. Twenty-one turned out to be quasars, one a compact galaxy, six low-redshift stars, and one undetermined. Redshifts in this sample of quasars are strongly concentrated around z =2, unlike redshift distributions in most previous samples of radio selected quasars. This is possibly a result of the faint apparent flux densities of the radio sources. Most surprising is that the present sample averages about 0.3 mag redder in B - V and U - B than the standard redshift-color relation for quasars. It is concluded that these radio weak Westerbork quasars are intrinsically redder than those found in the 3 C, strong 4 C and Parkes radio source surveys. Three possible explanations are considered. First, the optical colors of quasars may somehow be correlated with intrinsic radio luminosity. Second, a possibility exists that, since these quasars are generally near spiral galaxies, the galaxies are strongly reddening background quasars over areas of many galaxy diameters beyond the visible galaxy disk. Finally, an analysis of radio sources from the Westerbork background source survey which have flux densities >8.1 mJy shows that Sb and Sc galaxies which liave non-equilibrium companions nearby have greater numbers of radio sources near them than do similar spirals without such companions. If this result is confirmed by a study of a larger sample, it would imply that some of the quasars measured here may be associated with these kinds of spirals. Key words: quasars - radio source survey - spectrophotometric observations
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- August 1979
- Bibcode:
- 1979A&A....77...86A
- Keywords:
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- Microwave Spectra;
- Quasars;
- Stellar Spectrophotometry;
- Astronomical Catalogs;
- Radio Astronomy;
- Radio Sources (Astronomy);
- Red Shift;
- Stellar Magnitude;
- Ubv Spectra;
- Astronomy;
- Quasars:Redshifts;
- Radio Sources:Optical Counterparts;
- Radio Sources:Spectrophotometry;
- Radio Sources:Surveys